A study of the wood anatomy of Picea abies roots and their role in biomechanical weathering of rock cracks

Abstract

Our study of the wood anatomy of roots of Norway spruce (Picea abies (L.) Karst) growing in fractured bedrock reveals widening of bedrock cracks. Analysis, under a transmitted-light microscope of 30 micro-sections of three roots from two trees, shows that the most common anatomical features of roots growing in fractured bedrock are the blocking of radial growth, multi-directional uneven radial growth and fan-shaped deformation of cell rows. Crack widening is indicated by a sequence of features: normal growth followed by blocking of radial growth, then reappearance of radial growth. Changes in crack shape are shown by formation of traumatic resin ducts followed by radial growth eccentricity or multidirectional uneven growth. Eccentricity and radial growth release and an abrupt decrease in cell size imply increasing space for root growth and root exposure. We found inconclusive evidence of crack widening due to pressure from increasing root size (biomechanical weathering). Nevertheless, root anatomy indicates sudden crack widening, with other possible causesincluding tree-trunk flexing of roots by strong winds, mass-movement or freeze-thaw processes.